Nuclear magnetic resonance has been shown to be a useful, non-perturbative tool for studying model membrane systems. However, application to biological membranes has been limited by the broad line widths (short spin-spin relaxation times) and, for certain nuclei, long acquisition times (long spin-lattice relaxation times) which are found for these systems. In these repsects biological membranes are similar to solids and methods which have been developed for solid state NMR can be used to study biological membranes. We propose to spin samples at the magic angle and use proton enhanced nuclear induction spectroscopy, to obtain resolved NMR spectra for biological membranes. P31 NMR will be used to study the role of lipids in membrane function. The experiments will measure asymetry in lipid distribution between the two sides of the membranes, changes in membrane surface properties as reflected in the interactions of the lipid head groups, and the mobility of the phosphate portion of the lipid molecules. These measurements will be used to monitor the effects of viral transformation, cell cycle, cholesterol depletion, alteration of muscle-like proteins, and the action of various membrane active agents (e.g. hormones, Ca ions, antibiotics) on the distribution, interactions and mobility of membrane lipids. N15 NMR will be used to study the mechanism of active transport in the halobacterium halobium purple membrane. The protonatable nitrogens of the purple membrane protein will be selectively enriched in N15. The N15 NMR spectra of intermediates in the photoreaction cycle will be examined for chemical shift changes reflecting changes in protonation which might be associated with light-induced translocation of protons.